1. Field of the Invention
The present invention relates to an ink-jet recording head, and especially to the ink-jet recording head which can realize the higher density arrangement of ink nozzles.
2. Description of the Related Art
A non-impact recording method attracts public attention because this method is excellent in negligibly small noise at the time of recording. The ink-jet recording method included in the non-impact recording method has the advantages that a high speed recording is possible directly on a recording medium by using a simple mechanism. An ordinary paper can be used as the recording medium.
The ink-jet recording method is conducted by directly adhering ink droplets ejected from a recording head directly onto recording paper for recording letters and fingers. The ink-jet recording method has the advantages of conducting the recording without special fixation treatment to the ordinary paper in addition to conducting the high speed recording. A variety of ink-jet printers are proposed and commercialized.
A main stream of the ink-jet printers in recent days includes a piezoelectric element which converts an electric signal into mechanical energy as a pressure applying means for ejecting ink hereinafter referred to as xe2x80x9cpiezoelectric typexe2x80x9d. Still another embodiment of such printers includes a heater converting an electric signal into thermal energy as the pressure-applying means (hereinafter referred to as xe2x80x9cthermal typexe2x80x9d). The basic structures and operations of both of the printers of the piezoelectric type and the thermal type are not different except for the pressure-generation system, and only the piezoelectric type will be described.
A conventional ink-jet recording head of the piezoelectric type is described in JP-A-3(1991)-15555, and the configuration of the ink-jet recording head described therein is shown in FIG. 1. The ink-jet recording head includes a nozzle plate 11 having ink nozzles 10, and an ink pool 15 is defined by the nozzle plate 11, an ink pool plate 12 and an ink supply plate 13. A plurality of pressure chambers 18 are defined by a pressure chamber plate 16 and a vibration plate 17. Each of the pressure chambers 18 is communicated to the ink pool 15 through an ink supply port 19, and the vibration plate 17 includes stripe piezoelectric elements 20 each corresponding to each of the pressure chambers 18. Although each of the components is shown as a single element in FIG. 1, one or more plates may be integrally formed. Signal lines for transmitting electric signals to the piezoelectric elements 20 and ink paths for filling ink in the ink pool 15 are omitted in the drawings.
The operational principle in accordance with the Juniomoruv effect in the ink-jet recording head will be described referring to FIGS. 2A and 2B. Each of the piezoelectric elements 20 includes a first electrode 22a on a side in contact with the vibration plate 17 and a second electrode 22b on the reverse side, and the piezoelectric elements 20 have a polarization directed in the plate thickness direction (in the direction xe2x80x9cPxe2x80x9d in FIG. 2A). The vibration plate 17 to which each of the first electrode 22a of the piezoelectric elements 20 is communicated and a switching circuit 23 to which each of the second electrodes 22b is communicated are communicated to one and the other terminals of a driving source 24, respectively.
When the switching circuit 23 is turned on upon the input of a print order, a voltage is applied to the corresponding piezoelectric elements 20 from the driving source 24, and the piezoelectric elements 20 becomes contracted in the direction (in the direction xe2x80x9cexe2x80x9d in FIG. 2B) perpendicular to the plate thickness direction due to the piezoelectric transversal effect. At this stage, an amount of the distortion at the first electrode 22a side of the piezoelectric elements 20 is smaller because the first electrode 22a side is fixed to the vibration plate 17 and has an electric charge. Thereby, the amounts of the distortion of the both surfaces of the piezoelectric elements 20 are different, and the piezoelectric elements 20 flexibly deforms in the plate thickness direction (in the direction xe2x80x9cfxe2x80x9d in FIG. 2B) to reduce the volume of the corresponding pressure chamber 18 thereby increasing the inner pressure of the pressure chamber 18.
In FIG. 3A showing the sectional view at the time of the operation of the ink-jet recording head in accordance with the above operation principle, the ink is filled in the ink pool 15, the ink supply port 19, the pressure chambers 18 and the ink nozzles 10. When the switching circuit 23 (FIGS. 2A and 2B) is turned on in accordance with the printing order under the circumstance, the ink in the printing chamber 18 is pressurized by the piezoelectric elements 20 (arrow xe2x80x9cgxe2x80x9d) as shown in FIG. 3B to be ejected through the ink nozzle 10 because the pressure is open to the ink nozzle 10 and the ink supply path 19 (arrows xe2x80x9ckxe2x80x9d and xe2x80x9cmxe2x80x9d).
When the switching circuit 23 (FIGS. 2A and 2B) is turned off as shown in FIG. 3C, the internal of the pressure chamber 18 returns to the initial state as shown in FIG. 3A because the application of the pressure by the piezoelectric elements 20 is released (arrow xe2x80x9chxe2x80x9d). At this stage, the pressure chamber 18 is refilled with the ink flowing from the ink pool 15 side by the ejection through the ink supply port 19 as shown by an arrow xe2x80x9cnxe2x80x9d to complete the series of operations. The series of the operations are repeated at the high speed to conduct the printing.
In the conventional ink-jet recording head, the reduction of the recording head area viewed from the ink ejection side is limited because a plurality of the pressure chambers 18 are flatly arranged and a minimum head width is desired which equals to the sum of the widths of the pressure chambers 18 and the intervals between the adjacent pressure chambers 18. Therefore, an area occupied by the pressure chambers increases with the increase of the number of the ink nozzles for responding to the high density, and the demand for the higher density of the ink nozzles and the miniaturization of the recording head are trade-off.
In view of the foregoing, an object of the present invention is to provide an ink-jet recording head which promotes a higher density of ink nozzles while realizing smaller dimensions for the ink-jet recording head.
The present invention provides an ink-jet recording head including: an ink pool; a plurality of pressure chambers each communicated to the ink pool; a plurality of ink nozzles each communicated to a corresponding one of the pressure chambers; and a plurality of piezoelectric elements each for ejecting ink droplets through a corresponding one of the ink nozzles by exerting a pressure to a corresponding one of the pressure chambers; the pressure chambers and the piezoelectric element being alternately stacked.
In accordance with the present invention, the pressure chambers are stacked with one another viewed from the ink ejection side because the pressure chambers having the piezoelectric element are arranged vertically or stepwise. Thereby, when the number of ink nozzles is increased for responding to the demand for a higher density, the area occupied by the pressure chambers can be reduced. A particularly advantageous structure of the recording head includes ink nozzles communicating with end zones of respective pressure chambers. Accordingly, the smaller dimensions and the higher density can be realized for the recording head.
The above and other objects, features and advantages of the present invention will be more apparent from the following description.